Towards Urban Digital Twins: A Workflow for Procedural Visualization Using Geospatial Data

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article presents a new approach to semi-automatically generate the buildings and other assets of urban areas, to aid the creation of digital twins, and develop a pipeline for improving analysis and real-time visualization that would help decision-makers.

The work is overall well explained and of great interest. Below are some observations:

1) Images 04 and 05 are not clearly explained in the text. Please clarify better what the following steps mean: Buffer, PP_00 (01, 02, ...).

2) When you talk about performance in section 3.3.3 it would be better to add a table with the reference hardware.

3) when you talk about any Python implementation without in-depth textual explanation in the text please add a reference to the relative Github page (if the source code is open source) or specify why you can not share the code (e.g., an embargo for commercial reasons).

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the Abstract, the authors write “The steps for a complete, end-to-end solution involve developing robust systems for building detection, rooftop recognition, and geometry generation and importing and visualizing data in the same 3D environment.” This sentence is disconnected from the previous text. Are these examples of the identified challenges? There is a greater issue which is that at least part of this information is not available in the paper. For instance, there is no information or discussion about rooftops.

In the Introduction, page 1, line 36, the authors write “In contrast, procedural model generation provides a more flexible workflow. It enables the automatic regeneration of the virtual built environment as new data becomes available, addressing one of the key limitations of conventional methods”. The authors should add a citation to support this affirmation.

In the Introduction, page 1, line 41, the authors write “Digital twins represent a city through its physical assets…”. Since DT can be used in many contexts, I suggest that the authors adapt the sentence to “Digital twins [can/allow to] represent a city through its physical assets”. Also, the sentence is confusing. As the name implies, a DT represents the city through digital replicas of its physical assets, not through their physical assets. Simple wording issue.

In the Introduction, page 1, line 44, the authors write “The VirtualCity@Chalmers outlines six characteristics a digital twin must possess…”. Sometimes the authors write without providing enough context. What is the VirtualCity@Chalmers?

In the Introduction, page 2, line 52, the authors write “in a game engine using Python”. Although it was mentioned in the Abstract, the authors should identify the game engine here as well and cite its website. Alternatively, the authors can write “using a game engine.” instead and specify Unreal Engine and Python later, in the Methods sections. Also, users should mention that they used the experimental Python Editor Script Plugin to use the Python scripting language in Unreal Engine.

In the Introduction, page 2, can the two sentences in lines 52-55 be combined to avoid repeating “flexible and efficient worflow”?

By the end of the introduction, page 2, the authors write “The proposed workflow and effective visualization techniques can improve decision-making…”. However, the authors were not explicit about which visualization techniques were used.

In the Related Work, line 72, the authors should add a citation for the “TU Delft’s 3Dfier, ArcGIS API for Python”.

In the Related Work, line 72, the authors mention two processes, but cite three different ones.

In the Related Work, line 89, the authors write “(areas of water and vegetation)”. Are these examples of semantic configurations or the ones available? Use e.g. for example or i.e. if it is the case.

In the Related Work, line 102, the sentence starts without context. The authors should link the sentence to the previous ones or set a new topic. For instance, by writing “Regarding the creation of city models, building footprints and digital elevation models are commonly used as data sets”.

In the Related Work, line 102, what is OpenStreetMap? Insert citation.

In the Related Work, line 118, the authors write “They showcased the different stages involved in building LoD 2 and 3 models and their potential extension to LoD 4 in the (near) future”. I cannot understand this sentence as it is written. Are the authors writing about generating the models that correspond to the second, third and fourth LOD for the GIS environment?

In the Related Work, line 121, the sentence starts without context.

In the Related Work, subsection “Towards procedural workflows”, the authors include the citation at the end of the sentence. However, in the previous subsection, they cite after the authors’ identification. The authors must follow only one of the approaches throughout the document. In other cases, the authors only indicate the citation without identifying the authors involved in the cited work (e.g., line 160). The authors must be coherent.

Do not start a sentence with a citation (e.g., line 199).

In the Related Work, I do not understand the sentence in lines 234-235. What areas?

In the Materials and Methods, line 287, the authors reference Figure 3. Does this make sense? Shouldn’t be Figure 1?

Below, the authors should describe and cite the “Feature Manipulation Engine (FME)”.

In line 292, why is world creation written as “world-creation”?

In the 3.1 World Creation, the authors identify the used datasets. The format of the datasets should be described. For instance, .shp files are named Shapefile, whilst TIF are Tagged Image Format.

In the 3.1 World Creation, the authors present their process and Figure 2. However, the processes are not clear. What are PP_00, PP_01 and PP_02? Also, what are the Unreal Engine specs for tiles?

In the 3.1 World Creation, the process presented in Figure 4 is not explicitly described in the text. What is the Buffer and Dissolve parts of the workflow? Also, the Gaussian function is only described below in line 354.

In line 374 there is a citation missing, the same in line 378.

In subsection 3.3.1. Isoline Data, the authors present their method for the processing and representation of the isoline. The authors should mention that in the following sections, a representation of the isoline is available.

In 4.1. World Creation, the authors should include a sentence to present the following subsections. Check all the existing situations.

In 4.1.2. Unreal Engine Workflow, the authors include two images without referencing them. All images must be referenced and described in the text. Also, after the title, there should be text instead of an image.

In Discussions and Conclusion, the authors write “This paper presents a workflow for the procedural generation of such virtual worlds using commonly available GIS data sets enabled through modern game engines”. However, the presented workflow is only compatible with Unreal Engine, as other modern game engines, such as Unity and Godot lack some of the technologies such as Niagara for the creation of particle systems. This is a wording issue. I advise the authors to write “… through the modern game engine Unreal Engine”.

In Discussions and Conclusion, the sentences between the lines 576-582 are redundant is some of their information.

In lines 585-587, the authors write “In contrast, the Unreal Engine environment and many programs used to generate the analysis results operate on a Cartesian coordinate system with different points of origin.” Actually, Unreal Engine works using a single point of origin, defining the (x=0, y=0, z=0) of the map. If the meshes are misaligned, the cause of the problem can be their pivot point, which must be adapted.  Would the authors care to explain what they meant by this sentence?

 

As the authors mention in lines 594-596, they are not creating a digital twin. They are building a procedural generation tool for creating cities, that might be used as base for an urban digital twin system. The implementation only allows for editor visualization and does not include any type of simulation features. This should be explicit when presenting the advantages.

Therefore, the title is very misleading and does not inform about the content of the paper. Procedural generation and data visualization of what? And why “Towards Digital Twins”? Procedural generation has been used intensively for years to create videogames environments and assets. The title must be more explicit.

Comments on the Quality of English Language

The authors should consider using the DT acronym for Digital Twin, as the concept is written more than 30 times throughout the document.

In the Abstract, the authors write “…procedurally generated context generation…”. This sentence seems redundant. An alternative can be “…the procedural generation of context…” or “…procedural context generation…”.

In the Abstract, the authors write “Finally, the integration of various types of large-scale urban analysis data for visualization”. The meaning can be understood, but the sentence seems incomplete.

In the Related work, line 59, the authors should avoid starting a sentence using a number.

In the Related Work, authors write in future form, such as “In this chapter, we will explore…”. I suggest that the present form is used. The chapter is already written and is the current one.

In the Related Work, line 77, the authors use the apostrophe to represent plural form of LoD. The authors should remove the apostrophe and write simply “LoD”.

In the Related Work, line 112 starts with a miswritten full stop mark.

In the Related Work, lines 146-147, the authors introduce the GIS and 3DCM acronyms. However, these expressions were already used in the text above.

In the Materials and Methods, lines 283, the authors write “The methodology described in this paper consists of two parts, a - World Creation and b - Data Visualization”. This sentence seems unprofessional for a scientific journal. Instead, I suggest that the authors write “The methodology described in this paper consists of two parts. They are the World Creation and the Data Visualization”.

Line 344, missing a full stop mark.

In subsection 3.2.1. Integration of Landscape Tiles, I advise the authors not to use the hyphen when listing. I suggest writing “First, the land-use boundaries…” and so on.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article introduces a unique approach for creating digital replicas of urban areas and visualizing data using Python and Unreal Engine. This innovative method has the potential to revolutionize city planning, architecture, and civil engineering by efficiently integrating various data sources, such as GIS data, to generate highly detailed 3D models of cityscapes that are significantly more dynamic than traditional methods.

 

While the article mentions its innovation, it could do an excellent job of explaining how its method differs from existing practices in the realm of digital replicas and urban visualization. There's potential for exploring the implications of digital twins in city planning beyond just describing the technical aspects of the workflow. Including more case studies or hypothetical scenarios showcasing how this research can be applied in urban contexts would address this gap.

 

Although from line 58-281 is vital as it is, I suggest comparing it with established methods and analyzing how it stacks up against existing techniques for generating and visualizing digital twins. This comparison would emphasize the benefits or enhancements this workflow offers regarding precision, intricacy, efficiency, and user-friendliness. It would validate the current methods being employed.

 

The section in line 565 should be split into two sections. Considering the complexity of the subject, it would be beneficial to provide detailed reflections in the result section. This will assist the authors in addressing the following aspects:

• Consider expanding on the potential societal and economic impacts of incorporating digital twins into urban planning. This discussion could include the influence of digital twins on policy development, city governance, and public involvement. By exploring these aspects, the study can provide a more comprehensive understanding of the implications of the proposed research.

• Integrating new technologies by considering how developing technologies like AI, IoT, and simulation methodologies could complement or improve the suggested workflow. Reflecting on these linkages may increase twin accuracy, efficiency, and utility.

• Explore the challenges and constraints encountered during the research process, reflect more on the limitations (line 583), data quality issues, and more regarding scalability obstacles (found in Section 2.1). Consider how these challenges affect future workflow applications and propose potential solutions or areas for future investigation.

For the conclusion: provide a summary and suggestions for future research based on the results and limitations. This will help offer more straightforward guidance on future research directions, which would be beneficial. This might involve improving workflow features, incorporating data visualization types, or exploring real-time data integration for dynamic digital twins.

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Thank you to the authors who have provided a very interesting paper. Overall I think the content, however, I also feel there is presentation improvements that should be made prior to its publication. My overall comments are:

 

-What is the overall research question you are attempting to answer? What is your testable aim - can you clarify this in the introduction

-How did you identify the topics for study in Section 2. 

-The methodology - Section 3, in my view - actually covers the methodology of your approach. But it should also consider the methodology of your research - how will you validate and test your approach?

-Please add a conclusion that will consider the consider the validation of the approach, but also should discuss possible impact of the work and future work.

Author Response

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Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

See the attached file.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

See in the attached file.

Author Response

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Author Response File: Author Response.pdf